Typical residential swinging (as compared to sliding) doors are either a single door or a double door, the latter often being known as a “French” door. A single door is the more secure of the two types of traditional doors, but single doors are still vulnerable based on the weak door frame construction.
A double door typically has a first door that can be unlockably secured to the door frame with pins in the top and bottom of the door that enter the door frame. A second door is locked in place by a traditional door lock and/or a deadbolt that interacts with a striker plate in the first door. The second door is difficult to secure because there is no door jam to aid in reinforcement.
It would be desirable to have a security device for a double door that can withstand substantial force (e.g., forced entry level force), yet be easily attached or removed. Such a door security device would be conveniently storable. It would also provide a shape that is aesthetically pleasing and that would not be overly prominent in presence.